Economical magnetic locator apparatus and method

Abstract

Magnetic locators for detection of buried objects, such as ferromagnetic objects, are disclosed. Inputs provided from one or more magnetic sensors, such as three three-axis magnetic sensors, as well as from other sensors, such as accelerometers and gyroscopic sensors, may be used to determine magnetic field distortion indicative of ferromagnetic objects and provide output information corresponding to the detected object.

We claim: 
     
       1. A magnetic locator device, comprising:
 a housing element; 
 a first three-axis magnetic sensor device disposed in the housing element; 
 a second three-axis magnetic sensor device disposed in the housing element, wherein the second three-axis magnetic sensor device is positioned above the first three-axis magnetic sensor device in the housing element when the housing element is in a vertical orientation; and 
 a circuit board module coupled to the first three-axis magnetic sensor device and the second three-axis magnetic sensor device, wherein the circuit board module is configured to compare output signals from the first three-axis magnetic sensor device and the second three-axis magnetic sensor device so as to determine a magnetic field distortion caused by a ferromagnetic object; wherein the device is configured so that the first three-axis magnetic sensor device and the second three-axis magnetic sensor device may be calibrated such that the measured B-field magnitudes from the first three-axis magnetic sensor device and the second three-axis magnetic sensor devices are matched in one or more magnetic field directions. 
 
     
     
       2. A magnetic locator device, comprising:
 a housing element; 
 a first three-axis magnetic sensor device disposed in the housing element; 
 a second three-axis magnetic sensor device disposed in the housing element, wherein the second three-axis magnetic sensor device is positioned above the first three-axis magnetic sensor device in the housing element when the housing element is in a vertical orientation; and 
 a circuit board module coupled to the first three-axis magnetic sensor device and the second three-axis magnetic sensor device, wherein the circuit board module is configured to compare output signals from the first three-axis magnetic sensor device and the second three-axis magnetic sensor device so as to determine a magnetic field distortion caused by a ferromagnetic object; wherein the output signals from the first three-axis magnetic sensor device and second three-axis magnetic sensor device are coupled through a differential op-amp circuit and a high-pass filter circuit to normalize the output signals. 
 
     
     
       3. A magnetic locator device, comprising:
 a housing element; 
 a first three-axis magnetic sensor device disposed in the housing element; 
 a second three-axis magnetic sensor device disposed in the housing element, wherein the second three-axis magnetic sensor device is positioned above the first three-axis magnetic sensor device in the housing element when the housing element is in a vertical orientation; and 
 a circuit board module coupled to the first three-axis magnetic sensor device and the second three-axis magnetic sensor device, wherein the circuit board module is configured to compare output signals from the first three-axis magnetic sensor device and the second three-axis magnetic sensor device so as to determine a magnetic field distortion caused by a ferromagnetic object; wherein the output signals from the first three-axis magnetic sensor device and second three-axis magnetic sensor device are coupled through a differential op-amp circuit and a Kalman filter circuit to normalize the output signals. 
 
     
     
       4. The device of  claim 3 , further comprising an accelerometer device, wherein the output is further based on an output from the accelerometer device. 
     
     
       5. The device of  claim 3 , further comprising a gyroscopic device, wherein the output is further based on an output from the gyroscopic device. 
     
     
       6. A magnetic locator device, comprising:
 a housing element; 
 a first sensor module comprising a plurality of three-axis magnetic sensor devices disposed in the housing element; 
 a second sensor module comprising a magnetic sensor device disposed in the housing element, wherein the second sensor module is positioned above the first sensor module in the housing element when the housing element is in a vertical orientation; and 
 a circuit board module coupled to the first sensor module and the second sensor module, wherein the circuit board module is configured to compare output signals from the first sensor module and the second sensor module so as to determine a magnetic field distortion caused by a ferromagnetic object. 
 
     
     
       7. The device of  claim 6 , wherein the magnetic sensor devices comprise anisotropic magnetoresistive (AMR) sensor devices. 
     
     
       8. The device of  claim 6 , wherein the plurality of three-axis magnetic sensor devices includes three three-axis magnetic sensor devices positioned substantially equidistantly around the interior of the housing element. 
     
     
       9. The device of  claim 6 , wherein an output of the second sensor module comprises a reference signal for computing magnetic field variations determined based on an output of the first sensor module. 
     
     
       10. The device of  claim 6 , further comprising an output element, wherein the output element is configured to provide an output associated with the ferromagnetic object based at least in part on the determined magnetic field variation. 
     
     
       11. The device of  claim 10 , wherein the output element comprises an audible indicator element disposed to provide an audible output associated with the ferromagnetic object. 
     
     
       12. The device of  claim 10 , wherein the output element comprises a display element, and the device further includes a display circuit component configured to receive a signal corresponding to the determined magnetic field distortion and generate a signal to control an output display associated with the ferromagnetic object, based at least in part on the determined magnetic field distortion, on the display element. 
     
     
       13. The device of  claim 12 , wherein the output display comprises a visual indication of a bearing to the ferromagnetic object. 
     
     
       14. A magnetic locator device, comprising:
 a housing element; 
 a first sensor module comprising a plurality of anisotropic magnetoresistive (AMR) sensor devices disposed in the housing element; 
 a second sensor module comprising a magnetic sensor device disposed in the housing element, wherein the second sensor module is positioned above the first sensor module in the housing element when the housing element is in a vertical orientation; and 
 a circuit board module coupled to the first sensor module and the second sensor module, wherein the circuit board module is configured to compare output signals from the first sensor module and the second sensor module so as to determine a magnetic field distortion caused by a ferromagnetic object; 
 wherein the device is configured so that the first sensor module and the second sensor module may be calibrated such that the measured B-field magnitudes are matched in one or more field directions. 
 
     
     
       15. The device of  claim 7 , wherein the output signals from the first sensor module and second sensor modules are coupled through a filter circuit to normalize the output signals. 
     
     
       16. The device of  claim 15 , wherein the filter circuit comprises a differential op-amp circuit and a high-pass filter circuit. 
     
     
       17. The device of  claim 15 , wherein the filter circuit comprises a differential op-amp circuit and a Kalman filter circuit. 
     
     
       18. The device of  claim 10 , further comprising an accelerometer device, wherein the output is further based on an output from the accelerometer device. 
     
     
       19. The device of  claim 10 , further comprising a gyroscopic device, wherein the output is further based on an output from the gyroscopic device. 
     
     
       20. A method of magnetically sensing an object, comprising:
 generating a first output signal from a first sensor module comprising a plurality of three-axis magnetic sensor devices disposed in a housing element; 
 generating a second output signal from a second sensor module comprising a magnetic sensor device disposed in the housing element, wherein the second sensor module is positioned above the first sensor module in the housing element when the housing element is in a vertical orientation; 
 generating a signal corresponding to a magnetic field distortion caused by the object by comparing the first output signal and second output signal; and 
 providing an output corresponding to the object based at least in part on the magnetic field distortion signal. 
 
     
     
       21. A non-transitory computer readable medium containing instructions for causing a processor to perform a method including:
 generating a first output signal from a first sensor module comprising a plurality of three-axis magnetic sensor devices disposed in a housing element; 
 generating a second output signal from a second sensor module comprising a magnetic sensor device disposed in the housing element, wherein the second sensor module is positioned above the first sensor module in the housing element when the housing element is in a vertical orientation; 
 generating a signal corresponding to a magnetic field distortion caused by the object by comparing the first output signal and second output signal; and 
 providing an output corresponding to the object based at least in part on the magnetic field distortion signal.